1. Field of the Invention
This invention relates generally to impact type moving carriage printers and more particularly to such printers which are required to operate reliably in the presence of external vibration and/or shock forces.
2. Description of the Prior Art
Servo control systems for positioning a print head relative to a print medium are generally known and typically employ a coded timing wheel or disc which is secured to the shaft of a stepper motor which is used to selectively position the carriage and accordingly the print head. Typical examples of such apparatus include: U.S. Pat. No. 3,573,589, entitled, "Position Servo System For A Motor Including Detenting At Destination", which issued to J. Berry on Apr. 6, 1971; U.S. Pat. No. 4,114,750, entitled, "Printer System Having Local Control For Dynamically Alterable Printing", which issued to H. S. Baeck, et al. on Sept. 19, 1978; U.S. Pat. No. 4,158,800, entitled, "Control System" which issued to J. R. Jahelka, et al. on June 19, 1979; U.S. Pat. No. 4,349,770, entitled, "Electronic Damping System", which issued to R. A. Ragen on Sept. 14, 1982; and U.S. Pat. No. 4,362,980, entitled, "Position Error Recovery and Motor Control System", which issued to H. Itzkowitz on Dec. 7, 1982. In the last mentioned patent, the present position of a stepper drive motor in a typewriter is tracked by generating a pair of sensor signals and converting these signals to digital signals, which digital signals are constrained to change in accordance with the predetermined pattern on a step by step or increment by increment basis. If the pattern is not followed precisely, the error is detected and a correction in position information can be made.
Accordingly, it is an object of the present invention to provide an improvement in the printing apparatus.
Another object of the invention is to provide an improvement in dot matrix type of impact printers.
A further object of the invention is to provide an improvement in dot matrix printers which are capable of operating in harsh environments.
And still another object of the invention is to reposition the carriage mounted print head of a dot matrix printer following any unintentional movement which may be caused by externally generated vibration and/or shock forces.